Fertigation and Conventional Potassium Application to Field Grown Potato in Lebanon: Perspective to Enhance Efficiency

In Lebanon, potato occupies a surface of 14,800 ha corresponding to 17% of the irrigated land. The Bekaa valley is the largest production area in the country, with more than 67% of total potato production located on prime land. This crop is generally fertilized by soil application and irrigated by sprinklers with rare implementation of drip systems. Spring and summer potatoes depend entirely on irrigation, with an average yield of 20-25 t/ha of fresh tubers. In general, potato is cropped within a rotation consisting of wheat-potato-vegetable or legume rotation. For adequate growth, potato requires large amounts of potassium and nitrogen. In clay soils rich in active minerals, K is subject to fixation, which requires improved application methods to reduce K loss. Instead of traditional broadcasting, increasing fertilizer use efficiency is achieved through improved application with side banding method or fertigation with soluble forms of fertilizers. Literature from the region indicated no response to added K fertilizers on clay soils containing 200 mg K/kg soil. This study aims at reviewing the results of research works conducted in Lebanon with K-fertilization of potato with different rates, application methods and irrigation techniques in two main agro climatic zones of the country. The review will compare between the use of potassium sulfate as banding in the soil and in the irrigation water by fertigation. In the first winter trial, the splitting into two application dozes gave the higher fresh tuber yield (16 t/ha) despite the absence of significant difference between treatments. Yet, significantly higher elite tubers were found in early K application treatment, indicating the beneficial use from accessible potassium if timed to the plant needs. Also, very late K application towards the physiological maturity stage had a little impact. Despite the low mobility of K in comparison with N, the split application was advantageous also in comparison with a large single application of potassium to initially K deficient soil. Indeed, the ratio of available potassium (exchangeable + dissolved in the solution) to the sum of bivalent Ca and Mg showed a clear dynamic increase with the splitting of potassium. In the second spring trial, a significant yield increase was observed in the K treatments in comparison with the control, despite the initial K level in the clay soil testing 280 mg/kg soil. Tuber yield increase was associated with significant tuber size improvement (up to 50%) of elite tubers as compared to the control. Monitoring of plant water status revealed an immediate stomato response in the K treated plots to